Answer:
The total equivalent units for direct materials for October is  4,200
Explanation:
The Concept of Equivalent Units measures the number of units completed in terms of input element introduced in the process.
The Equivalent Units are Calculated on the units ending that is on  the Units Completed and Units of Closing Work in Process
Note that materials are added at the beginning of the process
Units Completed
Are 100% complete in terms of Raw Materials
Equivalent units = 3900 × 100 % = 3900
Units of Closing Work in Process
Are 100% complete in terms of Raw Materials
Equivalent units = 30 × 100 % = 300
Total Equivalent Units = 3900+300 = Â 4,200